I recently flew to SAN and there were lots of UM (end of the school year). We were taxiing towards take off and the call button goes off, FA gets on PA and goes through the spiel "is the an emergency, etc" as we wait for a few minutes, it happens again. Apparently, some 8 yo UM really needed to go. She went back and got him and took him up the FC lav. No big deal, accident (ehem) averted and she was really good natured about it.